Edward O. Edney

Organosulfate Formation in Biogenic Secondary Organic Aerosol

Organosulfates of isoprene, alpha-pinene, and beta-pinene have recently been identified in both laboratory-generated and ambient secondary organic aerosol (SOA). In this study, the mechanism and ubiquity of organosulfate formation in biogenic SOA is investigated by a comprehensive series of laboratory photooxidation (i.e., OH-initiated oxidation) and nighttime oxidation (i.e., NO3-initiated oxidation under dark conditions) experiments using nine monoterpenes (alpha-pinene, beta-pinene, d-limonene, l-limonene, alpha-terpinene, gamma-terpinene, terpinolene, Delta(3)-carene, and beta-phellandrene) and three monoterpenes (alpha-pinene, d-limonene, and l-limonene), respectively. Organosulfates were characterized using liquid chromatographic techniques coupled to electrospray ionization combined with both linear ion trap and high-resolution time-of-flight mass spectrometry. Organosulfates are formed only when monoterpenes are oxidized in the presence of acidified sulfate seed aerosol, a result consistent with prior work. Archived laboratory-generated isoprene SOA and ambient filter samples collected from the southeastern U.S. were reexamined for organosulfates. By comparing the tandem mass spectrometric and accurate mass measurements collected for both the laboratory-generated and ambient aerosol, previously uncharacterized ambient organic aerosol components are found to be organosulfates of isoprene, alpha-pinene, beta-pinene, and limonene-like monoterpenes (e.g., myrcene), demonstrating the ubiquity of organosulfate formation in ambient SOA. Several of the organosulfates of isoprene and of the monoterpenes characterized in this study are ambient tracer compounds for the occurrence of biogenic SOA formation under acidic conditions. Furthermore, the nighttime oxidation experiments conducted under highly acidic conditions reveal a viable mechanism for the formation of previously identified nitrooxy organosulfates found in ambient nighttime aerosol samples. We estimate that the organosulfate contribution to the total organic mass fraction of ambient aerosol collected from K-puszta, Hungary, a field site with a similar organosulfate composition as that found in the present study for the southeastern U.S., can be as high as 30%.

Model Representation of Secondary Organic Aerosol in CMAQv4.7

Numerous scientific upgrades to the representation of secondary organic aerosol (SOA) are incorporated into the Community Multiscale Air Quality (CMAQ) modeling system. Additions include several recently identified SOA precursors: benzene, isoprene, and sesquiterpenes; and pathways: in-cloud oxidation of glyoxal and methylglyoxal, particle-phase oligomerization, and acid enhancement of isoprene SOA. NO(x)-dependent aromatic SOA yields are also added along with new empirical measurements of the enthalpies of vaporization and organic mass-to-carbon ratios. For the first time, these SOA precursors, pathways and empirical parameters are included simultaneously in an air quality model for an annual simulation spanning the continental U.S. Comparisons of CMAQ-modeled secondary organic carbon (OC(sec)) with semiempirical estimates screened from 165 routine monitoring sites across the U.S. indicate the new SOA module substantially improves model performance. The most notable improvement occurs in the central and southeastern U.S. where the regionally averaged temporal correlations (r) between modeled and semiempirical OC(sec) increase from 0.5 to 0.8 and 0.3 to 0.8, respectively, when the new SOA module is employed. Wintertime OC(sec) results improve in all regions of the continental U.S. and the seasonal and regional patterns of biogenic SOA are better represented.

Epoxide Pathways Improve Model Predictions of Isoprene Markers and Reveal Key Role of Acidity in Aerosol Formation

Isoprene significantly contributes to organic aerosol in the southeastern United States where biogenic hydrocarbons mix with anthropogenic emissions. In this work, the Community Multiscale Air Quality model is updated to predict isoprene aerosol from epoxides produced under both high- and low-NOx conditions. The new aqueous aerosol pathways allow for explicit predictions of two key isoprene-derived species, 2-methyltetrols and 2-methylglyceric acid, that are more consistent with observations than estimates based on semivolatile partitioning. The new mechanism represents a significant source of organic carbon in the lower 2 km of the atmosphere and captures the abundance of 2-methyltetrols relative to organosulfates during the simulation period. For the parametrization considered here, a 25% reduction in SOx emissions effectively reduces isoprene aerosol, while a similar reduction in NOx leads to small increases in isoprene aerosol.

Determination of Secondary Organic Aerosol Products from the Photooxidation of Toluene and their Implications in Ambient PM2.5

A laboratory study was carried out to investigate the secondary organic aerosol products from photooxidation of the aromatic hydrocarbon toluene. The laboratory experiments consisted of irradiating toluene/propylene/NOx/air mixtures in a smog chamber operated inthe dynamic mode and collecting submicron secondary organic aerosol samples through a sampling train that consisted of an XAD denuder and a ZefluorTM filter. Oxidation products in the filter extracts were treated using O-(2,3,4,5,6,-pentafluorobenzyl)-hydroxylamine (PFBHA) to derivatize carbonyl groups followed by treatment with N,O-Bis(trimethylsilyl)-acetamide (BSTFA) to derivatize OH groups. The derivatized products were detected with a positive chemical ionization (CI) gas chromatography ion trap mass spectroscopy (GC-ITMS) system. The results of the GC-ITMS analyses were consistent with the previous studies that demonstrated the formation of multi-functional oxygenates. Denuder results showed that many of these same compounds were present in the gas, as well as, the particle phase. Moreover, evidence was found for a series of multifunctional acids produced as higher order oxidation products of the toluene/NOx system. Products having nearly the same mass spectrumwere also found in the ambient environment using identical analytical techniques. These products having multiple acid and alcoholic-OH moieties have substantially lower volatility than previously reported SOA products of the toluene photooxidation and might serve as an indicator for aromatic oxidation in the ambient atmosphere.

Secondary organic aerosol formation from the oxidation of aromatic hydrocarbons in the presence of dry submicron ammonium sulfate aerosol

Abstract A laboratory study was conducted to examine formation of secondary organic aerosols. A smog chamber system was developed for studying gas–aerosol interactions in a dynamic flow reactor. These experiments were conducted to investigate the fate of gas and aerosol phase compounds generated from hydrocarbon–nitrogen oxide (HC/NOx) mixtures irradiated in the presence of fine (

Production of organic nitrates from hydroxide and nitrate reaction with propylene.

Measurements of the gas-phase production rates of ..cap alpha..-(nitrooxy)acetone, propylene glycol dinitrate (PGDN), 2-hydroxypropyl nitrate (2-HPN), and 2-nitrooxy)propyl alcohol (2-NPA) in a C/sub 3/H/sub 6//N/sub 2/O/sup 5//air dark reaction and a C/sub 3/H/sub 6//NO/sub x/ air irradiation are reported. The probable operative reaction mechanisms are discussed, and the branching ratios for peroxy radical reaction with NO via RO/sub 2/ + NO ..-->.. RONO/sub 2/ vs. RO/sub 2/ + NO ..-->.. RO + NO/sub 2/ are estimated for CH/sub 3/CH(OO)CH/sub 2/OH and CH/sub 3/CH(OH)C-H/sub 2/OO radicals.

Thermodynamic modelling of aqueous aerosols containing electrolytes and dissolved organic compounds. II. An extended Zdanovskii–Stokes–Robinson approach

The Zdanovskii-Stokes-Robinson (ZSR) equation, or linear isopiestic relation, can be used to estimate osmotic and activity coefficients of multicomponent mixtures, based on the properties of pure (single solute) solutions. We have generalised an extension to the ZSR equation (for ternary mixtures) to systems containing an indefinite number of solutes, and derived the corresponding equations for solute activity coefficients. The new model is tested by calculating salt solubilities in Na+/NH4+/Cl-/SO42- aqueous solutions, liquid-liquid phase equilibrium in the acetone/glycerol/water system, and thermodynamic properties of aqueous NaCl/sucrose solutions (all at 298.15 K). The mixture parameters, up to three for each pair of solutes, significantly increase the accuracy of the method. It is least satisfactory for solutions containing both electrolytes and non-electrolytes, and it was found that the ZSR equation predicts activity coefficients of trace amounts of non-electrolytes in salt solutions that do not conform to the Setchenow relationship.

Density functional theory derived intermediates from the OH initiated atmospheric oxidation of toluene

Abstract A series of density functional based quantum mechanical calculations were carried out to identify potential intermediates produced by the OH addtion initiated atmospheric photo-oxidation of toluene. The potential for formation was assessed based on the relative stabilities of the assumed products. The calculations are consistent with OH addition occurring mainly at the ortho position, followed by addition of O2 at the meta position and formation of a bridged structure across the 1–3 position. In addition, the calculations suggest that carbonyl compounds containing epoxide structures may form during the oxidation.

Carbon monoxide production in photooxidation of organic molecules in the air

Sources and sinks of atmospheric carbon monoxide have not been in balance. The estimated rates of CO removal have been as much as a factor of two higher than estimated rates of emission. These discrepancies are much reduced when one considers the atmospheric photooxidation of the non-methane organic material released by vegetation. From known oxidation mechanisms it has been inferred that these photo-oxidations might be the largest single source of atmospheric carbon monoxide. A laboratory confirmation of this expected high CO yield is reported in this paper. Recognizing this large CO source allows the source-sink budgets to be balanced in both hemispheres, with due regard to isotope measurements, lifetime estimates and the inter-hemispheric CO concentration gradient. If the average OH radical concentration is 4 × 105 radicals cm−3, the source-sink balance indicates that the non-methane organic matter is producing in the Northern hemisphere 5.1 × 1014gy−1 CO (46% of the total), and in the Southern hemisphere, 2.5 × 1014gy−1 (50% of the total).

Acetaldehyde: the mutagenic activity of its photooxidation products

The authors exposed Salmonella typhimurium strain TA100 to the gas-phase products of the photooxidation of acetyldehyde by using the effluent from a flow-mode smog chamber. The total mutagenic activity of the photooxidation products under simulated atmospheric reaction conditions was measured. Significant mutagenic activity was observed when the reaction time was long and considerable concentrations of ozone and organic peroxy-type products were present and when the reaction time was short and the major products were formaldehyde and peroxyacetyl nitrate (PAN). The photoxidation of acetaldehyde is shown to account for a significant fraction of the mutagenic activity observed from the photooxidation of propylene. It was found that most of the observed response can be accounted for by the presence of PAN in the reaction chamber. The apparent mutagenic activity of PAN in the reaction chamber. The apparent mutagenic activity of PAN in these experiments was found to be considerably larger than in previous laboratory measurements. 12 references, 4 tables, 2 tables.